19Cr-9Ni-1.4Mo-1.4W-Nb 綱の応力リラクセーションに及ぼす再負荷の影響(<小特集>高温強度小特集)

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Empirical equations to describe reloading stress relaxation data were proposed in the previous papers8)9) on both ferritic and martensitic bolting steels. In this paper, application of the equations proposed was discussed to austenitic 19Cr-9Ni-1. 4Mo-1. 4W-Nb bolting steel which shows a peculiar stress relaxation behavior caused by structural changes during test^<10)11)>. Reloading stress relaxation tests on the steel were carried out at 650℃ and at the initial stress (σ_0) of 29. 3 kgf/mm^2 which corresponds to the value of stress for the total strain of 0. 20 percent. Repeated loadings were undertaken up to forty-five times at specific reloading time intervals (t_i=24, 72, 240 and 720 hours), and at specific residual stresses (σ_<rj>=0. 9σ_0, 0. 8σ_0, 0. 7σ_0, 0. 6σ_0, 0.5σ_0, 0. 46σ_0 kgf/mm^2). It was confirmed that the reloading stress relaxation curves of the present steel could not be represented by the creep constitutive equations as mentioned in the previous papers. The reloading stress relaxation data obtained for the steel showed a decrease in relaxation strength with increasing loading cycles except for the earlier numbers of loadings. Moreover, the specimens with specific residual stresses lower than 0. 7σ_0 resulted in failure. Their fracture mode was of intergranular type caused by linkage of grain boundary cavities.From examinations of accumulated plastic strain data, it was confirmed that slightly modified equations to describe the reloading stress relaxation data were applicable to the present steel. The modified equation for specific reloading time intervals data is log(σ_0-σ_<rj>)=a_0+a_1log t_i+a_2(log t_i)^2+a_3log N For specific residual stresses data, the expression is the same as the previous one : log t_j=b_0+b_1log(σ_0-σ_<rj>)+b_2{log(σ_0-σ_<rj>)}^2+b_3log N where σ_<rj> is the residual stress, t_j is the testing time, N is the number of loadings, and a_0, a_1 a_2, a_3, b_0, b_1, b_2, b_3 are constants.
社団法人日本材料学会の論文
1981-05-15

19Cr-9Ni-1.4Mo-1.4W-Nb 綱の応力リラクセーションに及ぼす再負荷の影響(<小特集>高温強度小特集)

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